This invention relates generally to power operated saws and deals more particularly with a precision woodworking saw having a variable speed drive system for transmitting power to the saw blade.
U.S. Pat. No. 4,503,742 discloses a precision saw which is particularly useful in the production of woodwork having various ornamental patterns and other intricate shapes. In the operation of the saw, some of the cuts which are to be made require relatively fast movement of the saw blade, while other cuts can be made more desirably with the saw blade set at a lower speed. Accordingly, it is desirable for the speed at which the saw blade is reciprocated to be adjustable.
Electronic devices are usually provided on saws of this type to control the speed of the blade. Although electronic speed controllers function well in many applications, they are not particularly well suited for use on reciprocating saws. Because of their relatively high cost, electronic devices add significantly to the overall cost of the saw. Also, the reciprocating action of the saw can create noticeable vibration which can damage electronic components and destroy electrical connections. Significant costs are encountered in repairing or replacing electronic speed control devices that are damaged as a result of vibrational forces. In addition, the entire saw must be taken out of production while the repair of a damaged speed controller or installation of a new speed controller is taking place. The downtime of the machine creates delays that can be costly in terms of production losses.
The present invention is directed to a precision saw which is equipped with a mechanical variable speed drive arrangement that is less expensive and more reliable and durable than the speed controllers that have been used in the past in reciprocating arm saws.
It is an important object of the invention to provide a precision woodworking saw having a variable speed drive mechanism that is constructed to withstand vibration of the saw without significant adverse effects. The mechanical components which are used in the drive system are better able to tolerate vibrational forces than the more delicate electronic components that are used in electronic drive systems and controllers.
Another object of the invention is to provide a precision saw having a variable speed drive mechanism which permits the speed of a reciprocating saw blade to be adjusted in a continuous manner over a wide range of speeds. Due to the use of split pulleys in the drive system, the speed ratio between the drive shaft and driven shaft can be adjusted continuously and is not restricted to discrete steps as are some types of drive systems.
A further object of the invention is to provide a precision saw in which the variable speed drive mechanism has a compact construction and is well suited to be incorporated in existing saw designs.
An additional object of the invention is to provide a precision saw in which the variable speed drive can be quickly and conveniently adjusted to set the desired speed of the saw blade. The speed adjustment requires only the turning of a knob, and the knob is mounted at a conveniently accessible location on the saw where it can be easily reached and adjusted to vary the speed.
Yet another object of the invention is to provide, in a precision saw of the character described, a variable speed drive mechanism which is highly durable and reliable and which operates accurately to allow the speed to be finely adjusted.
A still further object of the invention is to provide a precision saw in which the variable speed drive mechanism is simple and economical to construct and install.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.